NFPA Journal

Even though NFPA 72®, National Fire Alarm and Signaling Code®, provides guidance on fire alarm system design issues for assembly occupancies, designers still have a responsibility to investigate the existing or potential conditions in new assembly occupancies to ensure detection and notification systems are adequate.

A good place to start is the 2018 edition of NFPA 101®, Life Safety Code®, which defines an assembly occupancy as one used for “a gathering of 50 or more persons for deliberation, worship, entertainment, eating, drinking, amusement, awaiting transportation, or similar uses,” or as a “special amusement building, regardless of occupant load.” The code contains 24 examples of assembly occupancies, ranging from armories to theaters, all of which share some characteristics such as high ceilings and high ambient noise levels. In designing, installing, and maintaining fire detection and notification of a fire emergency, both identified attributes present issues with which designers, installers, and maintainers must deal.

Specifically, the high ceiling environment will have the greatest impact on early detection. Most designers do not specify a fire size at which they expect detection to occur. However, depending upon the detection method chosen, the high ceiling will require a sizable fire to initiate detection. Regardless, most designers already know that spot-type smoke detectors have proven inefficient for early detection on high ceilings. Depending upon the type of fuel available, a much larger fire is needed to actuate ceiling-mounted spot-type detectors on a ceiling that exceeds 30 feet.

Linear-projected-beam-type smoke detectors offer the best design choice for most high-ceiling environments. If the building stores high-value materials on shelves that might slow the rise of heat and smoke, a designer may choose an aspirating detection system installed in each row of shelving to meet the detection goals and expectations of the owner. Most owners and other stakeholders expect “early detection” of any fire, but because stakeholders often misunderstand the concept of early detection, designers must carefully explain the design limitations of various types of detectors.

Notifying occupants presents a second common element of concern in assembly buildings. Depending upon the actual type of assembly occupancy, NFPA 101 may require a fire emergency voice alarm communication system, or EVACS. Even if the code does not require an EVACS, stakeholders may desire the features those systems provide. The 2016 edition of NFPA 72 also permits the use of a fire EVACS for paging and music distribution. As a result, we find more system designers recommending fire EVACS even when the building codes may not require such a system.

For example, when a large assembly occupancy has only staff present, management may wish to page individuals in addition to warning them of an emergency. The message of such paging must have intelligibility. If a fire emergency occurs in the building, the stakeholders want to automatically notify the occupants, again with intelligible messages. This would drive the request for the installation of a fire EVACS to meet both needs.

Additional considerations for audibility and intelligibility include determining the ambient noise levels and the additional noise level of the operations. Many assembly occupancies have hard surfaces that generate reverberation and audio feedback that can greatly affect intelligibility and detract from the emergency messaging the stakeholders wish to provide the occupants.

For smaller assembly occupancies, it makes sense to ensure that non-voice fire alarm notification appliances meet the audibility requirements of the code.

The guidance provided by NFPA 72 on these design issues is valuable, but it is intended to supplement what a designer learns from a thorough investigation of the conditions in a new assembly occupancy. Ultimately, the design of the fire alarm system must meet both the design intent and the goals of the stakeholders.

WAYNE D. MOORE is vice president at Jensen Hughes.